Diphosphines

Abstract

 A disphosphine of the general Formula I


wherein
   R and R³ independently from each other represent an alkyl, cycloalkyl, aryl or aryl-alkyl group or an aryl group which is substituted at the aromatic ring with one or more halogen, alkyl and/or alkoxy radical,
   R⁴ represents an alkylene, cycloalkylene, arylene or aryl-alkylene group or an arylene group which is substituted at the aromatic ring with one or more halogen, alkyl and/or alkoxy radical; and
   A is -C(O)-, -S(O)₂-, -S(O)- or a divalent group comprising
-C(O)-, -S(O)-,


The disphosphines are useful for stabilizing thermoplastic polymers, such as polycarbonates, against thermal discoloration.

Description

[0001] The present invention relates to a diphosphine, a process for preparing it and to the use of the diphosphine for stabilizing a thermoplastic polymer against thermal discoloration. Furthermore, the present invention relates to a polymer composition containing a thermoplastic polymer and the diphosphine.

[0002] It is generally known in the art that most of the known thermoplastic polymers are affected to a certain extent when they are exposed to heat. The deterioration of the polymers often results in yellowing of the polymer and in degradation of its molar mass. Therefore, it is common to treat thermoplastic polymers with stabilizers. A large variety of stabilizers have been suggested in the prior art for the various thermoplastic polymers.

[0003] It has been suggested to utilize certain organic phosphites, phosphonites or phosphines, optionally in combination with epoxides or polydialkylsiloxanes, for stabilizing polycarbonates against oxidative, thermal and actinic degradation.

[0004] For example, U.S. Patent No. 4,092,288 discloses color stable polycarbonate compositions consisting of an aromatic polycarbonate resin having in admixture therewith 0.005 to 0.5 weight percent of a triaryl, trialkyl, tri(alkylaryl) or alkyl-aryl phosphine, preferably triphenylphosphine.

[0005] U.S. Patent No. 4,627,949 discloses a process for preparing shaped articles from polycarbonates stabilized with phosphanes by a devolatilizing injection-moulding or extrusion process. The phosphanes have the Formula (R)₂PR¹ wherein R is an unsubstituted or substituted C₆-C₁₄-aryl radical and R¹ = R or an unsubstituted or substituted C₁-C₁₈-alkyl radical.

[0006] U.S. Patent No. 4,835,202 discloses the use of (hydroxyphenyl)phosphine derivatives for stabilizing a wide variety of polymers-against oxidative, thermal and actinic degradation.

[0007] Unfortunately, the suggested stabilizers are volatile at the high temperatures which are applied for extruding polycarbonates.

[0008] U.S. Patent No. 4,145,525 discloses polyalkylene carbonates of improved thermal stability. At least a portion of the free hydroxyl groups is reacted with a hydroxyl reactive phosphorus compound whereby the active hydrogen on the hydroxyl group is replaced by an oxygen-phosphorus bond. Unfortunately, the oxygen-phosphorus bond can be easily hydrolyzed by acids. Accordingly, the end-capped groups are relatively instable in the presence of acids. However, traces of acids are often present when polycarbonates are washed and later extruded.

[0009] U.S. Patent No. 4,474,937 discloses phosphorus-modified polyester carbonates resins. The repeating unit within the polymer can be a phosphonite, phosphite, phosphonate or phosphate species. The amount of phosphorus present in the polymer is 1 to 1000 ppm, preferably 1 to 100 ppm, based on the weight of the polymer. The resins exhibit improved thermal-oxidative stability compared to non-modified polyester carbonates.

[0010] U.S. Patent No. 4,444,978 discloses the preparation of carbonate polymers having increased thermal stability by incorporating into the polymer chain an oligomer which has the Formula:

[0011] H-[O-R-O-P(OR₁)]_n-O-R-OH. R is the divalent residue of a dihydric mononuclear or a dihydric polynuclear phenol, R₁ is an alkyl, aralkyl or alkaryl group having 1 to 25 carbons, and n is a number having an average value of 1to 200. From 10 to 2000 ppm, preferably from 100 to 1000 ppm of the oligomer are copolymerized with the copolymer.

[0012] Although a wide variety of stabilizers exist for the various types of thermoplastic polymers, it is still desirable to provide new stabilizers in order to meet the ever increasing quality requirements for thermoplastic polymers.

[0013] One object of the present invention is to provide new compounds which can be used for stabilizing thermoplastic polymers, such as polycarbonates, against thermal discoloration. It is a preferred object of the present invention to provide a new stabilizer for thermoplastic polymers which is less volatile at high temperatures than the phosphines and phosphanes disclosed in U.S. Patent Nos. 4,092,288 and 4,627,949.

[0014] One aspect of the present invention is a diphosphine of the general Formula I:


wherein
   R and R³ independently from each other represent an alkyl, cycloalkyl, aryl or aryl-alkyl group or an aryl group which is substituted at the aromatic ring with one or more halogen, alkyl and/or alkoxy radicals,
   R⁴ represents an alkylene, cycloalkylene, arylene or aryl-alkylene group or an arylene group which is substituted at the aromatic ring with one or more halogen, alkyl and/or alkoxy radicals, and
   A is -C(O)-, -S(O)₂-, -S(O)- or a divalent group comprising -C(O)-, -S(O)-,

[0015] Another aspect of the present invention is a process for preparing the diphosphine of Formula I wherein a compound of Formula II


wherein R, R³, R⁴ have the meanings indicated above, is reacted with a compound of Formula:

        X - A - X   (III)


wherein A has the meaning indicated as above and each X independently is halogen, hydroxy or alkoxy or, both X's together are an anhydride group.

[0016] Yet another aspect of the present invention is the use of the diphosphine of Formula I for stabilizing a thermoplastic polymer, such as a polycarbonate, against thermal discoloration.

[0017] Yet another aspect of the present invention is a method of stabilizing a thermoplastic polymer against thermal discoloration, which method comprises contacting the thermoplastic polymer with an effective amount of a diphosphine of Formula I.

[0018] Yet another aspect of the present invention is a polymer composition which comprises a thermoplastic polymer, such as a polycarbonate, and a diphosphine of Formula I. The polymer composition may be in various forms, for example in the form of granules or pellets or in the form of a molded article.

[0019] In the diphosphine of the general Formula I


   R and R³ independently from each other represent an alkyl, cycloalkyl, aryl or aryl-alkyl group or an aryl group which is substituted at the aromatic ring with one or more such as halogen, alkyl and/or alkoxy radicals,
   R⁴ represents an alkylene, cycloalkylene, arylene or aryl-alkylene group or an arylene group which is substituted at the aromatic ring with one or more such as halogen, alkyl and/or alkoxy radicals, and
   A is -C(O)-, -S(O)₂-, -S(O)- or a divalent group comprising -C(O)-,


-S(O)-, -P(O)- or

[0020] The radicals R and R³ can be identical or different.

[0021] Of the alkyl and alkylene groups those are preferred that have 1 to 18, preferably 1 to 12 carbon atoms. The alkyl and alkylene groups can be straight-or branched-chain. The most preferred alkyl groups are methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl or tert-butyl or the pentyl, hexyl, octyl, nonyl, decyl or octadecyl groups. The most preferred alkylene groups are methylene, ethylene, n-propylene, i-propylene, n-butylene, sec-butylene or tert-butylene or the pentylene, hexylene, octylene, nonylene, decylene or octadecylene groups.

[0022] Of the cycloalkyl and cycloalkylene groups those having 5 or 6 carbon atoms are preferred, such as cyclopentyl or cyclohexyl, cyclopentylene or cyclohexylene.

[0023] Of the aryl and arylene groups those having from 6 to 14 carbon atoms are preferred, such as phenyl or naphthyl, phenylene or naphthylene. The aryl and/or arylene groups may be substituted with one or more of the above-mentioned alkyl groups and/or with one or more halogens, such as fluoro, chloro or bromo, and/or one or more alkoxy groups. Alkoxy groups, if present, preferably contain 1 to 6 carbon atoms, such as the methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, sec. butoxy or tert. butoxy groups. If substituted, the aryl and/or arylene groups preferably are substituted with 1, 2 or 3 substituent groups.

[0024] In the aryl-alkyl groups the above-mentioned alkyl groups are preferred and the aryl group preferably is phenyl. Preferred aryl-alkyl groups are benzyl, phenyl butyl, tolyl or xylyl.

[0025] In the aryl-alkylene groups the above-mentioned alkylene groups are preferred and the aryl group preferably is phenyl. Preferred aryl-alkylene groups are benzylene, phenyl butylene, tolylene or xylylene.

[0026] If R⁴ is cyclohexyl, phosphorus and oxygen are preferably bound in the 1,4-position to the cyclohexyl group. If R⁴ is an optionally substituted phenylene group, phosphorus and oxygen are preferably arranged in the para-position to the phenylene group.

[0027] Preferably, R and R³ are aryl groups, most preferably phenyl, and R⁴ is an arylene group, most preferably phenylene. The aryl and/or arylene groups preferably have from 6 to 14 carbon atoms. They are preferably unsubstituted or substituted at the aromatic ring with one or more halogens, such as bromo or chloro, one or more alkyl groups, such as the above-mentioned C₁₋₆-alkyl groups, and/or one or more alkoxy groups, such as methoxy, ethoxy, propoxy and/or butoxy groups.

[0028] Preferably A is -C(O)-, -S(O)₂-, -S(O)- or a divalent group comprising -C(O)-, -S(O)-,


or


Preferred A groups are -C(O)-, -S(O)-, -S(O)₂-, -C(O)-alkylene-C(O)- or -C(O)-arylene-C(O)-, wherein the arylene group is optionally substituted at the aromatic ring with one or more of the radicals halogen, alkyl, cycloalkyl, aryl, oxyalkyl, hydroxy, alkoxy and/or -C(O)-[O-R⁴-P(R)(R³)] and the alkylene group is optionally substituted with one or more of the radicals halogen, alkyl, cycloalkyl, aryl, oxyalkyl, hydroxy, alkoxy and/or -C(O)-[O-R⁴-P(R)(R³)].

[0029] If A comprises an alkylene group, it is preferably unsubstituted or substituted with one or more alkyl and/or alkoxy groups. Preferred alkoxy groups are listed above. The most preferred alkyl groups are methyl, ethyl, n-propyl or, most preferably, isopropyl. These alkyl groups provide branching to the alkylene group. The alkylene group preferably comprises from 1 to 50, more preferably from 3 to 30, most preferably from 4 to 25 carbon atoms. Most preferably, it is linear and unsubstituted.

[0030] If A comprises an arylene group, it is preferably a phenylene group which is optionally substituted at the aromatic ring with one or more halogens, alkyl, cycloalkyl and/or alkoxy groups. Preferred halogens and alkyl, cycloalkyl and alkoxy groups are described above. The most preferred arylene group is phenylene which is preferably unsubstituted or substituted with one or more of the above-mentioned C₁₋₆-alkyl groups, C₅₋₆-cycloalkyl groups, bromo, chloro, methoxy, ethoxy, propoxy and/or butoxy groups. If A comprises an optionally substituted phenylene group, it is preferably the 1,4-phenylene group.

[0031] Alternatively, A is the group


-Si(R⁹)[O-R⁴-P(R)(R³)] or -Si[O-R⁴-P(R)(R³)]₂, wherein R⁶, R⁷, R⁸ and R⁹ independently from each other represent an alkyl, cycloalkyl, aryl or aryl-alkyl group or an aryl group which is substituted at the aromatic ring with one or more halogens, alkyl, cycloalkyl, aryl, oxyalkyl, hydroxy or alkoxy groups. Preferred alkyl, cycloalkyl, optionally substituted aryl and aryl-alkyl groups are the same as those listed above for R¹ and R.

[0032] Particularly preferred diphosphines of Formula I are those wherein R and R³ are phenyl, R⁴ is phenylene and A is -C(O)-phenylene-C(O)- or -C(O)-alkylene-C(O)-, wherein the alkylene group comprises from 3 to 20 carbon atoms.

[0033] It has been found that the diphosphines of the present invention are considerably less volatile at elevated temperatures than corresponding known phosphines which only comprise one group (R)(R³)P-. Particularly, the diphosphines of the present invention are less volatile at temperatures which are usually maintained during processing of polycarbonates, that is, at temperatures of more than about 200°C. Due to their lower volatility, less powerful equipment, such as ventilation, is required to keep the concentration of these compounds in air below a certain level. Furthermore, it has been found that several diphosphines of the present invention are as effective as the corresponding known monophosphines for stabilizing thermoplastic polymers, such as polycarbonates, against thermal discoloration. Surprisingly, it has been found that some of the diphosphines of the present invention are even more effective stabilizers than the corresponding monophosphines.

[0034] By the term "diphosphines" is meant that the compounds of the present invention comprises at least two groups (R)(R³)P-R⁴-. Depending on the meaning for A in Formula I above, the compounds of Formula I may even comprise three or more of these groups.

[0035] Another aspect of the present invention is a process for preparing a diphosphine of Formula I wherein a compound of Formula II


is reacted with a compound of Formula III

        X - A - X   (III)


wherein R, R³, R⁴ and A have the meanings as indicated above and each X independently is halogen, hydroxy or alkoxy or, both X's together are an anhydride group.

[0036] If R⁴ in Formula II is an optionally substituted phenylene ring, the hydroxy group in Formula II may be arranged in ortho-, meta- or para-position to the phosphorus, however, it is preferably arranged in para-position to the phosphorus.

[0037] Compounds of Formula II and methods of preparing them are known in the art, for example, from U.S. Patent No. 4,835,202 and from the references cited therein.

[0038] Preferred meanings for X in Formula III are bromine, alkoxy and, more preferably, chlorine. If X is an alkoxy group, it preferably contains 1 to 6 carbon atoms, such as the methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, sec-butoxy or tert-butoxy group.

[0039] Preferred compounds of Formula III are phosgene, SO₂Cl₂, dichlorodialkylsilanes and aromatic or aliphatic diacid chlorides. The most preferred compounds of Formula III are phosgene, terephthalic acid dichloride, dichlorodimethylsilane and saturated, unsubstituted aliphatic diacid chlorides comprising from 1 to 30, preferably from 1 to 20, more preferably from 3 to 20 carbon atoms in the alkylene group.

[0040] The molar ratio between the compound of Formula II and the compound of Formula III generally is at least 1.7:1, preferably from 1.9:1 to 2.2:1, more preferably from 2 to 2.1:1, most preferably 2:1.

[0041] Depending on the specific starting materials which are used in the reaction, an acid may be produced as a by-product. For example, HCl is produced when X in Formula III is chlorine. In such a case, preferably a base is added to the reaction mixture for neutralizing the acid. Preferably, the molar number of basic groups is at least 1, more preferably from 1.5 to 2 per mole of chlorine radical in the compound of Formula III. The preferred types of base mainly depend on the type of diluent that is used for the reaction.

[0042] The reaction temperature preferably is from 20°C to 100°C, more preferably from 20°C to 70°C, most preferably from 25°C to 50°C, depending on the reaction diluent. The reaction is preferably conducted at about ambient pressure.

[0043] Depending on the type of reaction diluent, the reaction can be conducted a) as a two-phase process or b) in a homogeneous solution.

[0044] For conducting a two-phase process, the reaction diluent comprises an aqueous and an organic phase. The volume ratio between the aqueous phase and the organic phase preferably is from 1:2 to 2:1, more preferably from 1:1.5 to 1.5:1, most preferably 1:1. The interphase surface area preferably is from 0.1 m/l to 50 m/l. The reaction diluents are preferably water and one or more water-immiscible solvents, preferably one or more chlorinated solvents. Preferred chlorinated solvents are chlorobenzene, dichlorobenzene, ethylene chloride or, most preferably, methylene chloride. The most useful bases are alkali hydroxides or alkaline earth hydroxides, such as NaOH, KOH, CsOH, Ca(OH)₂, Mg(OH)₂ or the corresponding oxides which form hydroxides when contacted with water, such as CaO. The two-phase process is particularly suitable if phosgene is used in the reaction.

[0045] For conducting the reaction in a homogeneous solution, generally one or more organic solvents are used which are inert towards the reactants and which are preferably polar. Preferred organic solvents are chlorinated solvents, such as chlorobenzene, dichlorobenzene, ethylene chloride or, most preferably, methylene chloride; ethers, such as dimethyl ether, tetrahydrofuran, dimethoxyethane or, most preferably, dioxane; formamides, such as dimethylformamide or dimethylacetamide; esters, such as acetic ester; or ketones, such as acetone. Most preferably, chlorinated solvents and/or ethers are used. Preferred bases are amines, more preferably tertiary aliphatic amines, such as trimethylamine or triethylamine, or aromatic amines, such as pyridine.

[0046] The above-described process i) is particularly suitable if A is -C(O)-, -S(O)-, -S(O)₂-, -C(O)- alkylene-C(O)-, -C(O)-arylene-C(O),


or


the alkylene and arylene group optionally being substituted as described above.

[0047] If A is the group




or -Si[O-R⁴-P(R)(R³)]₂, the compounds of Formula I can be produced by the above-described process i), however they are preferably produced as described below.

[0048] A compound wherein A is


is preferably produced by reacting a compound of Formula II and P(O)X₃, preferably POCl₃, in a molar ratio of more than 2.5:1, more preferably at least 3:1, most preferably from 3.0 to 3.1:1.

[0049] A compound wherein A is


is preferably produced by reacting a compound of Formula II and Si(R⁹)X₃, preferably Si(R⁹)Cl₃, in a molar ratio of more than 2.5:1, more preferably at least 3:1, most preferably from 3.0 to 3.1:1.

[0050] A compound wherein A is


is preferably produced by reacting a compound of Formula II and SiX₄, preferably SiCl₄, in a molar ratio of more than 3.5:1, more preferably at least 4:1, most preferably from 4.0 to 4.1:1.

[0051] Depending on the type of reaction diluent, the reaction can be conducted a) as a two-phase process or b) in a homogeneous solution, as described above for process i).

[0052] Useful reaction temperatures, pressure, bases and reaction diluents are those described with respect to process i) above.

[0053] The diphosphines of Formula I of the present invention are very effective for stabilizing thermoplastic polymers against discoloration. Accordingly, another aspect of the present invention is a polymer composition which contains one or more thermoplastic polymers and one or more of the above-described diphosphines of Formula I. The polymer composition of the present invention preferably comprises from 0.001 to 2.5 weight percent, more preferably from 0.01 to 0.5 weight percent, most preferably from 0.02 to 0.2 weight percent of one or more of the diphosphines of Formula I, based on the weight of the thermoplastic polymer. If the polymer composition of the present invention comprises more than one diphosphine of Formula I, their total weight preferably is within the indicated range.

[0054] The thermoplastic polymer preferably is a polyolefin, such as an ethylene-homo- or copolymer or a polypropylene, a polyacrylate, polymethacrylate or poly (methyl/methacrylate) or a styrene-homo- or copolymer, such as polystyrene, a styrene/acrylate copolymer, a copolymer of styrene, butadiene and an acrylonitrile, (an ABS polymer), a polycarbonate or a blend of such polymers. The stabilizer composition of the present invention is particularly useful for stabilizing a polycarbonate which is optionally blended with an ABS (acrylonitrile/butadiene/styrene) polymer, a polyester, such as polyalkyleneterephthalate, preferably polyethyleneterephthalate, a polystyrene, a polyarylene-sulphone or with a polyolefin. Preferred polyolefins are polyethylene or ethylene copolymers, such as ethylene/propylene copolymers, ethylene/acrylate copolymers, polypropylene, polybutene, polyisobutene or polymethylpentene. These polymers are well known in the art.

[0055] For the sake of convenience in the following paragraphs mainly polymer compositions are described which contain a polycarbonate as a thermoplastic polymer, although the present invention is not limited thereto. Suitable polycarbonates are described in U.S. Patent No. 4,722,955, column 2, lines 6-42 and the references cited therein. The thermoplastic polycarbonates present in the polymer compositions of the present invention generally are polycondensates which are obtainable by reacting a diphenol with a carbonate precursor, such as phosgene, a haloformate, an acid chloride, preferably a difunctional acid chloride, such as terephthalic acid chloride, or a carbonate ester. Aromatic polycarbonates are preferred.

[0056] Preferred diphenols are those of Formula HO-Z-OH, wherein Z comprises a mononuclear or polynuclear aromatic group of 6 to 30 carbon atoms, to which the hydroxy groups are directly linked. The aromatic group may comprise a heteroatom and may be substituted with one or more groups, for example one or more halogens and/or one or more alkyl or cycloalkyl groups. Preferred diphenols are hydroquinone, resorcinol, dihydroxybiphenylenes, bis(hydroxyphenyl)alkanes, bis(hydroxyphenyl)cycloalkanes, bis(hydroxyphenyl)fluorenes, bis(hydroxyphenyl)ethers, bis(hydroxyphenyl)sulfides, bis(hydroxyphenyl)ketones, bis(hydroxyphenyl)sulfones, bis(hydroxyphenyl)sulfoxides and alpha,alpha'-bis(hydroxyphenyl)diisopropylbenzenes and derivatives thereof which are halogenated and/or alkylated at the nucleus. Other examples of suitable diphenols which are useful as starting materials for the polycarbonates are listed in U.S. Patent No. 4,627,949, column 2, line 68 to column 3, line 22, in U.S. Patent No. 4,962,144, column 2, lines 17-46 and in European Patent Application EP-A-0 423 562, p. 2, lines 24-55 and p. 3, lines 1-19. Preferred diphenols are 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, 4,4'-dihydroxydiphenyl, 1,1-bis-(4-hydroxyphenyl)-cyclohexane, 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 1-phenyl-2,2-bis(4-hydroxyphenyl)propane (phenyl-substituted bisphenol A), 9,9-bis-(4-hydroxyphenyl)fluorene and, most preferably, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A). Mixtures of two or more different diphenols may be used, for example a mixture comprising 3 to 97 weight percent of bisphenol A and 97 to 3 weight percent of another bisphenol.

[0057] Most preferably, the polycarbonate is prepared from bisphenol A and phosgene. The polymer composition of the present invention preferably contains an aromatic, transparent polycarbonate.

[0058] Polycarbonates and methods of producing them are well known in the art. For example the polycarbonate can be prepared by a homogeneous organic solution process, a melt process or, preferably, a known interfacial two-phase process. U.S. Patent No. 4,092,288 discloses aromatic polycarbonates and methods of preparing them in column 4, lines 4-68 and in Example 1. Alternatively, polycarbonates can be prepared from diphenylcarbonate or dimethylcarbonate by transesterification. These processes are described by D. Freitag et al., Encyclopedia of Polymer Science and Engineering, Vol. 11, pp. 651-654 and the references cited therein.

[0059] Branched polycarbonates are also suitable. If the polycarbonate is branched, it preferably contains from 0.01 to 3 percent, more preferably from 0.05 to 2 percent of a branching agent, based on the weight of the polycarbonate. Branched polycarbonates, methods of preparing them and suitable branching agents are, for example, described in the published European Patent Application EP-A-0 423 562, p. 3, line 43 to p. 4, line 2. Useful branching agents have three or more functional groups, preferably three or more phenolic hydroxyl groups. Preferred branching agents are 1,3,5-tris(4-hydroxyphenyl)benzene, 1,1,1-tris(4-hydroxyphenyl)ethane, tris(4-hydroxyphenyl)phenylmethane and 2-(4-hydroxyphenyl-2-(2,4-dihydroxyphenyl)propane. Other useful branching agents are trimesic or trimellitic acid or acid chlorides, 2,4-dihydroxybenzoic acid, cyanuric chloride or 3,3-bis(4-hydroxy-3-methyl phenyl)2-oxo-2,3-dihydroindol.

[0060] Blends of a linear polycarbonate and a branched polycarbonate are also suitable.

[0061] The polycarbonates preferably have a number average molecular weight of from 10,000 to 250,000, more preferably from 12,000 to 120,000 and most preferably from 15,000 to 45,000.

[0062] The end groups of the polycarbonate may be the same or different. The most preferred end groups are p-tert-butylphenyl, p-octyl phenyl, or phenyl. End groups which can lead to a cross-linking of polycarbonate such as arylcyclobutene-terminated carbonate polymers are particularly useful. Known chain terminators can be used, such as tert-butylphenol, phenol or other C₁₋₇-alkyl phenols. Other preferred chain stoppers and their useful amounts are disclosed in European Patent Application EP-A-0 423 562, p. 4, lines 5-21.

[0063] The diphosphines of the present invention are particularly efficient when the polymer composition of the present invention contains an inorganic or organic light diffuser. Light diffusers are generally used for introducing light-scattering properties into transparent polymers. Polymer compositions containing light diffusers are widely used in the electrical and lighting industry, for example as luminaries. Unfortunately, many of the known light diffusers are sensitive towards heat and/or oxygen. Surprisingly, it has been found that the above-described diphosphines are very efficient for stabilizing a thermoplastic polymer against thermal discoloration, even when a light diffuser has been compounded into the polymer.

[0064] If present, the polymer composition generally contains a light diffuser in an amount of from 0.1 to 10 weight percent, preferably from 0.2 to 5 weight percent, more preferably from 0.5 to 3 weight percent, based on the weight of the thermoplastic polymer, such as polycarbonate.

[0065] Preferred inorganic light diffusers are barium sulphate, titanium dioxide and blends thereof.

[0066] Organic light diffusers and methods of preparing them are known, for example from German Offenlegungsschrift 21 46 607. Preferred organic light diffusers are known from the published European Patent Application EP-A-0,269,324. This light diffuser comprises particles of a core/shell morphology which have an average diameter of from 2 to 15 micron, a particle size distribution such that at least 90 percent by weight of the particles fall within ±20 percent of the average particle diameter, a core of rubbery alkyl acrylate polymer, the alkyl group having from 2 to 8 carbon atoms, copolymerized with 0 or up to 5 percent cross-linker and 0 or up to 5 percent graft-linker (based on the total weight of the core), and one or more polymer shells. The shells comprise from 5 to 40 percent of the weight of the particles. All the shells or only the outer most shell are preferably a polymer of an alkyl methacrylate, a vinyl arene, a vinyl carboxylate and/or an alkyl acrylate. Further details on the light diffuser comprising particles of a core/shell morphology and methods of preparation are disclosed in European Patent Application 0,269,324.

[0067] The average particle diameter of the organic light diffuser generally is from 0.1 to 100 microns, preferably from 1 to 15 microns. The particles are preferably of spherical shape.

[0068] The polymer composition of the present invention may contain optional additives, such as optical brighteners or fluorescent dyestuffs, pigments or colorants, tackifiers, mold release agents, impact modifiers, or fillers. Such optional additives are generally known in the art. If present, the polymer composition of the present invention contains an optical brightener or a fluorescenting dye preferably in an amount of from 0.01 to 3 weight percent. The amount of pigments or colorants preferably is from 0.0001 to 5 weight percent, if present at all. Preferred mold release agents are known esters of long fatty acids; their preferred amount is from 0.01 to 2 weight percent. Preferred fillers are glass fibers, their preferred amount is from 1 to 30 weight percent. All percentages are based on the weight of the thermoplastic polymer in the polymer composition.

[0069] The polymer composition of the present invention may contain one or more other heat stabilizers, antioxidants, and/or UV stabilizers, such as phosphites, hypophosphites, phosphonites or, preferably, one or more hindered phenols. Hindered phenols and their use as antioxidants are described in Ullmann's Encyclopedia of Industrial Chemistry, Volume 3, "Antioxidants," pp. 95-98, 5th ed., 1985, VCH Verlagsgesellschaft mbH and in Encyclopedia of Polymer Science and Engineering, Volume 2, "Antioxidants" pp. 75-91, 1985 by John Wiley & Sons, Inc. If present, the amount of such an additive generally is from 0.01 to 5 percent, preferably from 0.05 to 2 percent, more preferably from 0.1 to 1 percent, based on the weight of the thermoplastic polymer in the polymer composition. An additional heat stabilizer may be present, depending on the type of thermoplastic polymer. For example, if the polymer composition is substantially comprised of a polycarbonate, the presence of an additional heat stabilizer may be advantageous. If a polycarbonate is blended with a substantial amount of another thermoplastic polymer like polyolefins, vinyl-containing polymers, such as polymethyl methacrylates, the presence of an additional heat stabilizer is generally not necessary. If an additional heat stabilizer is used, its amount is generally only 0.01 to 0.5 percent, based on the weight of the thermoplastic polymer.

[0070] For preparing the polymer composition of the present invention an effective amount of the diphosphine of Formula I is mixed with the thermoplastic polymer. Effective amounts are indicated further above. One or more optional additives, such as an above-described light diffuser, may be mixed with the thermoplastic polymer prior to, simultaneously with or after the addition of the diphosphine of Formula I. The mixing temperature is not very critical. Room temperature is the most convenient one, however, decreased or elevated temperatures are also useful. However, it is advisable to mix the diphosphine with the thermoplastic polymer, which may contain optional additives such as a light-diffuser, before the thermoplastic polymer is processed to granules or pellets. Most preferably, the diphosphine is admixed before the thermoplastic polymer is subjected to any processing or compounding step at elevated temperature. The manner of dispersing or mixing the diphosphine(s) of Formula I and any optional additives with the thermoplastic polymer(s) is not critical. However, the process chosen should be one which results in a great degree of dispersion of all the additives throughout the thermoplastic polymer. Preferred mixing equipment are mixing rolls, ribbon blenders, dough mixers or Banbury mixers. The mixture can then be processed to granules or pellets by known extrusion techniques. The mixture may be fed into an extruder and extruded to a strand which is then granulated into pellets or granules. A preferred method is a devolatilizing extrusion process as generally described in U.S. Patent No. 4,627,949. If the polymer composition contains a polycarbonate, the extrusion is preferably conducted at a temperature of from 200°C to 390°C, more preferably from 230°C to 380°C, most preferably from 260°C to 370°C.

[0071] The pellets or granules may be formed into shaped articles in a generally known manner, for example by compression molding, injection-molding or casting techniques. A preferred processing method is a devolatilizing injection-molding as generally described in U.S. Patent No. 4,627,949. If the polymer composition contains a polycarbonate, the injection-molding is preferably conducted at a temperature of from 200°C to 380°C, more preferably from 230°C to 370°C, most preferably from 260°C to 370°C. Examples of shaped articles are sheets and lamp covers.

[0072] The invention is further illustrated by the following examples which should not be construed to limit the scope of the present invention. Unless otherwise stated all parts and percentages are by weight.

Examples 1 to 9 and Comparative Examples A to M

[0073] Several physical properties are measured as follows:

[0074] The Melt Flow Rate (MFR) is measured according to ASTM D 1238-88.

[0075] The Yellowness Index number (YI) is measured according to ASTM D 1925-70. The Yellowness Index number is an indication of discoloration of the polycarbonate composition. The lower the number, the lower is the yellowness of the polycarbonate composition due to discoloration.

[0076] The total light transmittance and light diffusion are measured according to ASTM D-1003.

[0077] The following stabilizers are used in the Examples and Comparative Examples:

Stabilizer I: Bis(diphenyl 4,4'-hydroxyphenyl phosphine) carbonic acid ester prepared according to Example 1 below.

Stabilizer II: Bis(diphenyl 4,4'-hydroxyphenyl phosphine) terephthalic acid ester prepared according to Example 2 below.

Comparative Stabilizer III: Triphenylphosphine.

Comparative Stabilizer IV: Tetrakis-(2,4-di-tert-butylphenyl)-4,4'-triphenylene-diphosphonite, commercially available as Sandostab™ PEPQ.

Comparative Stabilizer V: 1,4-Bis(diphenylphosphino)butane, available from Aldrich.

Stabilizer VI: Bis(diphenyl 4,4'-phenoxy phosphine) dimethyl silane.

Example 1

Preparation of the Diphosphine

[0078] Bis(4,4'-hydroxyphenyl diphenyl phosphine) carbonic acid ester, that is, a compound of Formula I wherein R and R³ were phenyl, R⁴ was phenylene and A was C(O), was produced according to the following procedure:

[0079] A flask was fitted with a reflux condenser, a dropping funnel, an agitator, and an inlet pipe for nitrogen and for liquid addition. The system was flushed with nitrogen. 5.6 g of diphenyl 4-hydroxyphenyl phosphine were brought into the flask and flushed with nitrogen again. 20 mL of 1.5 molar caustic were purged with nitrogen and dropped into the flask. Then 12.5 mL of a 5 percent solution of bis(trichloromethyl)carbonate (which forms phosgene by rearrangement) in dichloromethane were slowly added. Then 2 mL of 10 percent caustic were added. A second portion of 12.5 mL of the solution of bis(trichloromethyl)carbonate in dichloromethane was added, followed by the addition of 20 mL of 10 percent caustic. Then 0.03 g of triethylamine in 20 mL of dichloromethane were added. The reaction was performed at 25°C. After completion of the reaction, the two phases of the reaction mixture were separated by gravimetric settling. A slight nitrogen purge was maintained during the purification procedure. The aqueous phase was removed from the flask. Then 20 mL of 10 percent aqueous hydrochloric acid was added into the flask and the mixture was agitated. After gravimetric settling and removal of the aqueous phase, the remaining phase was washed three times with 20 mL of water. Then dichloromethane and subsequently remaining traces of water were removed under vacuum. A white powder of bis(diphenyl 4,4'-hydroxyphenyl phosphine) carbonic acid ester was obtained.

[0080] The melting point Fp of the compound was 133°C, as measured by Differential Scanning Calorimetry. The structure of the compound was confirmed by IR, ¹H-NMR and ³¹P-NMR. The purity of the compound was more than 96 percent, the yield was 71 percent, based on the amount of diphenyl hydroxyphenyl phosphine.

[0081] IR-Spectroscopy: 1773 cm⁻¹ (C=O); 1586 cm⁻¹ (C-C aromate); 1492 cm⁻¹ (C-C aromate); 744 cm⁻¹ (mono-substituted aromate); 695 cm⁻¹ (mono-substituted aromate).

[0082] ¹³-C-NMR (in CDCl₃): 121, 128, 132, 133 and 135 ppm (aromatic), 151 ppm (C=O, ester-bond).

[0083] ³¹-P-NMR (in CDCl₃): -6.25 ppm (Singulett, phosphine) (calibrated with H₃PO₃.

[0084] The weight loss of the compound at elevated temperatures was measured by TGA (Thermal Gravimetric Analysis) at 10°C/minute under nitrogen. The weight loss is as follows:

Temperature (°C)	Weight loss (%)
300	5.5
393	32
440	54
562	85

[0085] The comparison with triphenylphosphine showed that the compound of the present invention was much less volatile than triphenylphosphine at temperatures which were usually used for extruding polycarbonates. Triphenylphosphine volatilizes completely at TGA test conditions at 300°C.

Use of the Diphosphine as a Stabilizer

[0086] Polycarbonate pellets prepared by interfacial polycondensation of bisphenol A and phosgene were used as a base resin. The polycarbonate had a melt flow rate of 3.3, a violet-blue color and a Yellowness Index of 1.4. 1000 ppm of Cetiol™ as a tackifier was homogeneously distributed on the polycarbonate pellets. Then 2.25 percent of barium sulphate (commercially available as K3 from Sachtleben), 150 ppm of titanium dioxide, 4000 ppm of Tinuvin™ 234 as a UV stabilizer, 1300 ppm of Uvitex™ as an optical brightener and a heat stabilizer of the type and concentration listed in Table I below were added. The mixture of the polycarbonate pellets and the additives was thoroughly shaken in order to homogeneously distribute the additives on the pellets. All amounts of the additives were based on the weight of the polycarbonate. The mixture was extruded to granules at a temperature of 365°C. The extrusion was carried out under vented conditions (300 rpm, 55 to 65 percent torque, double screw). The granules were injection-molded at 300°C into test bars of 3.2 mm thickness. The optical properties of the test bars are listed in Table I.

Example 2

Preparation of the Diphosphine

[0087] Bis(diphenyl 4,4'-hydroxyphenyl phosphine) terephthalic acid ester, that is, a compound of Formula I wherein R and R³ were phenyl, R⁴ was phenylene and A was C(O)-1,4-phenylene-C(O), was produced according to the following procedure: 5.6 g of diphenyl 4-hydroxyphenyl phosphine were brought into a flask of the type used in Example 1 and flushed with nitrogen. Then 40 mL of dichloromethane and 2 g of triethylamine were added under agitation. After complete dissolution of the diphenyl 4-hydroxyphenyl phosphine, 2.03 g of terephthaloyl chloride, dissolved in 20 mL of dichloromethane were dropped into the flask. The reaction was performed at a temperature of 25°C. After completion of the reaction, the reaction mixture was further processed as described in Example 1. A white powder of bis(diphenyl 4,4'-hydroxyphenyl phosphine) terephthalic acid ester was obtained.

[0088] The melting point Fp of the compound was 156°C, as measured by Differential Scanning Calorimetry. The structure of the compound was confirmed by IR, ¹H-NMR and ³¹P-NMR. The purity of the compound was 97 to 98 percent, the yield was 69.4 percent, based on the amount of diphenyl 4-hydroxyphenyl phosphine.

[0089] IR-Spectrosopy: 1736 cm⁻¹ (C=O); 1583 cm⁻¹ (C-C aromate); 1491 cm⁻¹ (C-C aromate); 744 cm⁻¹ (mono-substituted aromate); 699 cm⁻¹ (mono-substituted aromate.

[0090] ¹³-C-NMR (CDCl₃): 128 ppm (aromate); 130 to 132 ppm (phenylene of the terephthaloyle-unit); 133, 135 ppm (aromate); 164 ppm (C=O, ester-bond).

[0091] ³¹-P-NMR (CDCl₃): -5.82 (Singulett, phosphine) (calibrated with H₃PO₃).

[0092] The weight loss of the compound is measured by the same method as in Example 1.

Temperature (°C)	Weight loss (%)
302	4
386	9.7
420	23.4
447	38
590	67.1

[0093] The comparison with triphenylphosphine showed that the compound of the present invention was much less volatile than triphenylphosphine which volatilizes completely at TGA test conditions at 300°C.

Use of the Diphosphine as a stabilizer

[0094] Test bars were prepared in the same manner as in Example 1, except that bis(diphenyl 4,4'-hydroxyphenyl phosphine) terephthalic acid ester was used as a stabilizer. The optical properties of the produced test bars are listed in Table I below.

Example 3 and Comparative Examples A to D

[0095] Test bars were prepared in the same manner as in Example 1, however other types and/or amounts of heat stabilizer were used, as listed in Table I below. The optical properties of the produced test bars are listed in Table I.

Example 4 and Comparative Example E

[0096] Test bars were produced in the same manner as in Example 3 and Comparative Examples A to D, however, 1 percent of an organic light diffuser was used instead of a combination of barium sulphate and titanium dioxide. The organic light diffuser was a polymer having a core of poly(butyl acrylate) and a shell of poly(methyl methacrylate). It is commercially available from Rohm and Haas under the trademark Paraloid EXL 5137.

[0097] Visual comparison between Example 3 and Comparative Examples A and B, which make use of triphenylphosphine as a stabilizer, shows that the test bar of Example 3 had the whitest color. This finding was confirmed by the lowest Yellowness Index. In the tests made for Comparative Examples A and B triphenylphosphine was detected at the die and at the extruder vent. In the test made for Example 3 the diphosphine could neither be detected at the die nor at the extruder vent.

Example 5 and Comparative Examples F to J

[0098] Polycarbonate pellets prepared by interfacial polycondensation of bisphenol A and phosgene and comprising 0.5 percent of a branching agent were used as a base resin. The polycarbonate had a melt flow rate of 3.0. The polycarbonate comprises 400 ppm of tri-(2,4--di-tert-butylphenyl)phosphite as an additional heat stabilizer. 1000 ppm of Cetiol™ as a tackifier was homogeneously distributed on the polycarbonate pellets. Then a stabilizer of the type and concentration listed in Table II below is added. All amounts of the additives were based on the weight of the polycarbonate. The mixture was extruded to granules at a temperature of 298°C. The granules were injection-molded at 300°C into test bars of 3.2 mm thickness. The Yellowness Index YI of the test bars are listed in Table II below.

TABLE II

(Comparative) Examples	Stabilizer Type / Content (ppm)	Yellowness Index YI
F	none	3.5
G	IV / 1000	3.3
H	V / 1000	4.2
5	II / 1000	3.0
I	III/ 1000	3.1
J	III / 2000	3.2

[0099] The results of Table 2 illustrate a diphosphine of the present invention (Example 5) was a considerably better heat stabilizer than the diphosphine of Comparative Example H. In these tests the Yellowness Index of the test bar produced according to Example 6 was even lower than the Yellowness index of the test bars produced according to Comparative Examples I and J which comprise triphenylphosphine as a stabilizer.

Example 6

Preparation of the Diphosphine

[0100] Bis(diphenyl 4,4′-phenoxy phosphine) dimethyl silane, that is, a compound of Formula I wherein R and R³ were phenyl, R⁴ was phenylene and A was -(CH₃)Si(CH₃)- was produced according to the following procedure: 5.6 g of diphenyl 4-hydroxyphenyl phosphine were brought into a flask of the type used in Example 1 and flushed with nitrogen. Then 40 mL of dichloromethane and 2 g of triethylamine were added under agitation. After complete dissolution of the diphenyl 4-hydroxyphenyl phosphine, 1.3 g of dichlorodimethylsilane, dissolved in 20 mL of dichloromethane were dropped into the flask. The reaction was performed at a temperature of 25°C. After completion of the reaction, the reaction mixture was further processed as described in Example 1. Bis(diphenyl 4,4'-phenoxy phosphine) dimethylsilane of light yellow color was obtained. The yield of the compound was 73.4 percent, based on the amount of diphenyl hydroxyphenyl phosphine.

[0101] ¹-H-NMR (CDCl₃, TMS): 0.41 ppm, (O-Si-CH₃); 6.75 to 6.9, 7.2 to 7.4 (phenylene).

[0102] ³¹-P (CDCl₃, H₃PO₃): -6.88 ppm (Singulett, phosphine).

Use of the Diphosphine as a Stabilizer

[0103] Polycarbonate pellets prepared by interfacial polycondensation of bisphenol A and phosgene were used as a base resin. The polycarbonate had a melt flow rate of 3.5 and a Yellowness Index of 1.9. 1000 ppm of the stabilizer VI of Example 6 were dispersed in 2000 ppm of Cetiol™ at 70°C. The dispersion was homogeneously distributed on the polycarbonate pellets. Then 2.25 percent of barium sulphate (commercially available as K3 from Sachtleben), 150 ppm of titanium dioxide, 4000 ppm of Tinuvin 234™ as a UV stabilizer and 1300 ppm of Uvitex™ as an optical brightener were added. All amounts of the additives were based on the weight of the polycarbonate. The mixture was extruded to granules and then injection-molded at 300°C into test bars in the same manner as in Example 1. The optical properties of the test bars are listed in Table III below.

Comparative Examples K to M

[0104] Test bars were prepared in the same manner as in Example 6, however only 1000 ppm of Cetiol™ were used as a tackifier (instead of 2000 ppm) and other types and/or amounts of stabilizer were used, as listed in Table III below. The optical properties of the produced test bars are listed in Table III below.

TABLE III

(Comparative) Exemples	Stabilizer Type / Content (ppm)	Total Light Transmittance	Light Diffusion	Yellowness Index YI
6	VI / 1000	62 %	51 %	10.4
K	none	60 %	50 %	19.4
L	IV / 1000	61 %	51 %	11.5
M	III / 1000	63 %	52 %	10.6

Claims

1. A diphosphine of the general Formula I

wherein
   R and R³ independently from each other represent an alkyl, cycloalkyl, aryl or aryl-alkyl group or an aryl group which is substituted at the aromatic ring with one or more halogen, alkyl and/or alkoxy radicals,
   R⁴ represents an alkylene, cycloalkylene, arylene or aryl-alkylene group or an arylene group which is substituted at the aromatic ring with one or more halogen, alkyl and/or alkoxy radicals, and
   A is -C(O)-, -S(O)₂-, -S(O)- or a divalent group comprising -C(O)-, -S(O)-, -S(O)-, -P(O)- or

2. The diphosphine of Claim 1 wherein A is -C(O)-, -S(O)-, -S(O)₂-, -C(O)-alkylene-C(O)- or -C(O)-arylene-C(O)-, the arylene group is optionally substituted at the aromatic ring with one or more of the radicals halogen, alkyl, cycloalkyl, aryl, oxyalkyl, hydroxy, alkoxy and/or -C(O)-[O-R⁴-P(R)(R³)], and the alkylene group is optionally substituted with one or more of the radicals halogen, alkyl, cycloalkyl, aryl, oxyalkyl, hydroxy, alkoxy and/or -C(O)-[O-R⁴-P(R)(R³)].

3. The diphosphine of Claim 2 wherein the alkylene group is a C₁₋₅₀-alkylene group which is optionally substituted with one or more alkyl or alkoxy groups and the arylene group is phenylene which is optionally substituted at the aromatic ring with one or more halogen, alkyl, cycloalkyl and/or alkoxy radicals.

4. The diphosphine of Claim 1 wherein A is the group



wherein R⁶, R⁷, R⁸ and R⁹ independently from each other represent an alkyl, cycloalkyl, aryl or aryl-alkyl group or an aryl group which is substituted at the aromatic ring with one or more halogen, alkyl, cycloalkyl, aryl, oxyalkyl, hydroxy and/or alkoxy radicals.

5. The diphosphine of any one of Claims 1 to 4 wherein R and R³ represent an aryl group and R⁴ represents an arylene group, the aryl and/or arylene groups being optionally substituted at the aromatic ring with one or more halogen, alkyl and/or alkoxy radicals.

6. The diphosphine of Claim 1 wherein R and R³ represent a phenyl group, R⁴ represents a phenylene group and A represents -C(O)- or -C(O)-phenylene-C(O)-.

7. A process for preparing a diphosphine of the general Formula I

wherein
   R, R³ and R⁴ and A have the meanings as indicated in any one of Claims 1 to 6, comprising the step of reacting a compound of Formula II

wherein R, R³ and R⁴ have the meanings as indicated in any one of Claims 1, 5 and 6
with a compound of Formula III

        X - A - X   (III)

wherein A has the meaning as indicated in any one of Claims 1, 2, 3, 4 and 6 and each X independently is halogen, hydroxy or alkoxy or, both X's together are an anhydride group.

8. A polymer composition comprising a thermoplastic polymer and a diphosphine of the general Formula I

wherein
   R, R³ and R⁴ and A have the meanings as indicated in any one of Claims 1 to 6.

9. The polymer composition of Claim 8 wherein at least a portion of the thermoplastic polymer is a polycarbonate.

10. The polymer composition of Claim 8 or 9 in the form of granules, pellets or in the form of a molded article.

11. The polymer composition of any one of Claims 8 to 10 comprising from 0.001 to 2.5 weight percent of one or more diphosphines of Formula I, based on the weight of the thermoplastic polymer.

12. A method of stabilizing a thermoplastic polymer against thermal discoloration, which method comprises contacting the thermoplastic polymer with the diphosphine of any one of Claims 1 to 6.